Formation of Two-dimensional Organic Polymers on a Mineral Surface

Abstract

ALTHOUGH a great many examples of naturally occurring and synthetic inorganic sheet polymers are known^1,2, very little work has been done on their organic counterparts. Planar organic macromolecules have attracted a considerable amount of interest because of the unusual properties they are expected to possess, but they have proved difficult to synthesize and there is a distinct lack of information about their properties. Synthesis may be approached either by carrying out the polymerization at an interface^3,4, or on a surface^5,6, or by using a monomer which for steric reasons is constrained to polymerize in two dimensions⁷. The polymerization of methyl meth-acrylate adsorbed in the interlayers of montmorillonite by means of γ-rays has been studied by Blumstein⁵. The resulting interlayer polymer was resistant to the usual solvent extraction procedures and could be isolated only by dissolving out the silicate lattice with hydrofluoric acid, a treatment liable to damage most polymers. From the dilute solution properties of the polymer it was deduced that the interlayer polymethyl methacrylate developed a two-dimensional sheet structure when a cross-linking agent was present during the polymerization⁸. I report here the results of attempts to prepare organic sheet polymers on the surface of a synthetic calcium aluminate hydrate of composition 4CaO·Al₂O₃·xH₂O (ref. 9). This mineral was selected because it can be made in a pure state, because it has a layer structure, and because it is capable of intercalating a wide range of organic materials⁹ and is soluble in dilute hydrochloric acid.